This invention relates to an apparatus for detecting faulty self-extinguishing switching elements coupled in series within a power conversion apparatus.
Apparatuses for detecting a fault of self-extinguishing switching elements, such as gate turnoff thyristors (GTO), connected in series within an inverter device, are known. Each of these apparatuses outputs signals of greatly different DC potentials upon detecting faulty switching elements. Such an apparatus is disclosed in, for example, U.S. Pat. No. 3,842,337 (Ekstoem et al.) and U.S. Pat. No. 3,878,448 (Jackson et al.) (All the technical disclosures of these U.S. patents are incorporated by reference in this specification.) In each of these conventional apparatuses, a plurality of element fault detectors are respectively coupled to series-connected thyristors, forming a thyristor rectifier of a high withstanding voltage. Each detector generates an output when it detects that the corresponding thyristor has a fault. The output is supplied to a protection control circuit through an optical fiber (i.e., a light guide). The optical fiber provides a DC isolation between the detector (at high potential) and the control circuit (at low potential).
Both conventional apparatuses have drawbacks. In a power conversion apparatus, the higher its withstanding voltage, and the greater its power capacity, the more thyristors must be connected in series to constitute one arm of each thyristor bridge, and the more detectors must be coupled to the thyristors. The apparatus will inevitably require more elements, and more optical fibers to transmit the output of the detectors.